1. Field of the Invention
This invention relates to improvements in a valve operating mechanism for a reciprocating engine, and more particularly to a valve lifter in the mechanism which lifter is made of fiber reinforced plastic and which is high in strength and durability.
2. Description of the Prior Art
A reciprocating internal combustion engine is provided with a valve operating mechanism for operating intake and exhaust valves in timed relation to engine revolution. A variety of valve operating mechanisms have been proposed and put into practical use. One of them is of the directly operating type wherein the valve stem of the intake or exhaust valve is directly operated through a metallic valve lifter by a rotating cam. A shim is disposed between the cam and the valve lifter to prevent wear of the valve lifter.
In such a valve operating mechanism, the valve lifter is required to be light in weight and high in strength, and additionally high in wear resistance since the valve lifter slidably moves along the inner surface of a bore formed in a cylinder head. In view of this, carburized steel has been hetherto used as the material of the valve lifter from the viewpoint obtaining high strength and wear resistance. Additionally, aluminum alloy has also been used as the material of the valve lifter from the viewpoint of lightening the weight of the valve lifter.
Recently, decreasing the inertial mass of an engine valve operating system has been becoming an important theme, aimed at improving the power output of the engine under decreasing friction and increasing engine speed. Accordingly, it is required to reduce the weight of the valve lifter.
In view of the above, studies have been conducted in which the valve lifter is formed of fiber reinforced plastic (FRP) which is high in specific strength as compared with conventional metallic materials.
However, difficulties are encountred in using such a plastic valve lifter, because there is the possibility of the valve lifter being cracked or broken during use. Particularly, cracking and breaking tends to occur in a part against which the shim is pressed under the rotating action of the rotating cam.